Lubricating grease compositions



Patente Dec. 3%, 1952 UNITED STAT OFFICE LUBRHJATHNG GREASE CUIVEPQSETIONS No Application September l, 1956), Serial No. 182,836

9 Claims.

This invention relates to lubricating grease compositions and more particularly to anti-friction bearing lubricating greases which are suitable for high temperature use. More par 'cularly, the invention relates to high temperature greases prepared from lubricating oil thickened with an alkali metal soap of a higher fatty acid, in conjLmcti-on with an alkali metal salt of a lower molecular weight oxy acid.

It has been suggested in the prior art that for a some purposes, it is advantageous to combine certain metal salts, particularly the metal salts of organic acids of low molecular weight, with the metal soaps which are ordinarily employed as thickeners for lubricating grease compositions. Various investigators have found that the addition of metal salts of the character referred to have utility for improving stability and high temperature properties, and the like. There appear to be several theories as to the operation of such metal salts in conjunction with the metal soaps. One such theory is that the addition of salts of low molecular weight acids to soaps of relatively high molecular weight results in the formation of a complex with superior grease thicken ng efiect and improved stability.

Whatevermay be the phenomena involved, the addition of salts of low molecular weight compounds appears to be particularly advantageous in connection with greases of alkali and alkaline earth metal soap bases. The low molecular weight salts appear in many cases to improve the physical structure of the grease. Compositions of this character are particularly receptive to the action of oxidation inhibitors and it is possible that the compositions themselves ar more stable against oxidation than greases thickened with soaps of high molecular Weight carboxylic acids alone, for example.

Suggestions in the prior art have included the use of metal salts of low molecular weight carboxylic acids which are saturated, such as acetic and propionic acids, and even more recently it has been suggested that certain of the lower unsaturated acids, such as acrylic acid, crotonic acid, and the like may be used as soap thickener adjuncts.

According to the present invention, the salts of certain low molecular Weight oxy acids are highly useful as ingredients of lubricating greases.

It is the object of this invention, therefore, to prepare an improved grease suitable for antifriction bearing and related surfaces at elevated temperatures, 1. e., temperatures in the neighborhood of from 300 F. to 350 F. and even higher. A further object of the invention is to provide a lubricating grease composition comprising a lubricating oil thickened to a grease consistency with a combination of the alkali metal soaps of high molecular Weight aliphatic acids and. alkali metal salts of lower molecular weight oxy acids, hereinafter to be described.

The low molecular weight oxy acids which are employed in this invention contain an ether linkage and in this respect are similar to furoic acid, which is a heterocyclic unsaturated acid containing an ether linkage in a 5-membered ring. In fact, greases prepared by employing salts of aikoXy acids such as ethoxypropionic acid, methoxybenzoic acid, and the like, are, in many respects, similar to the excellent high dropping point greases prepared from furoic acid; Other acids containing oxygen are apparently quite different. For example, when the soap of levulinic acid is employed, as the thickening agent alone or in combination with high molecular weight acid soaps, greases are formed of relatively low dropping point and poor structural characteristics. This would appear to be due to the oxygen atom of ketonic linkage contained in the levulinic acid molecule. The soaps of saturated straight chain acids of 6 to 10 carbon atoms having no oxygen in the hydrocarbon chain, such as caproic acid, do not form greases due to their difficulty of satisfactory dispersion. In addition, mixtures of soaps of levulinic acid and straight chain aliphatic acids are difiicult to disperse in mineral oil even at elevated temperatures, whereas the mixtures of the grease soaps and the salts of the oxy acids of this invention have a high degree of dispersibility.

Grease formulations containing the salts of the oXy aromatic acids-such as p-methoxybenzoic acid, have the added' advantage of a low degree of water solubility and will wet metallic surfaces covered with water. These grease formulations are also much more adhesive to metal surfaces than other type greases.

The structure of some of the cxy acids mentioned above are shown below:

Molecular Weight 118 CH3CH2OOHzGHz-GOOH Etho ypropionic acid. 112 O-CH=OHOH=CCOOH Furoic acid llG CHaCCHz-CHz-COOH Levulunc acid. 116 CH3--CH2-CHzCHr-CHz-COOH Caproic acid.

152 OH3OCOOH Anisic acid.

Ethoxypropionic acid may be prepared from In general, the grease should consist of a lubeta-propiolactone by reaction with ethyl alcohol. The beta-propiolactone may be prepared from formaldehyde and ketone. The preparation of this acid is described in the Journal of American Chemical Society, vol. 70, pages 998-1006 (1948). It may also be prepared by adding ethanol to acrylonitrile or acrylic esters followed by hydrolysis or by the reaction of an alkali eth'oxide with beta-halopropionic acid.

The oxy acid which are employed in the greases of this invention have the following general formula:

R representing a saturated aliphatic radical having from 1 to 5 carbon atoms such as methyl, ethyl, propyl, isopropyl, n-butyl, iso-butyl, sec. butyl, t-butyl, amyl, etc., or an aromatic radical having from 6 to 10 carbon atoms such as phenyl, tolyl, xylyl, t-butylphenyl, etc.; R representing a divalent radical as selected from the group above.

Specific mention may be made of such compounds as methoxypropionic acid, ethoxypropionic acid, nand isopropoxypropicnic acid, nand isopropoxyacetic acid, secondary-butoxyacetic acid, p-methoxybenzoic acid, p-ethoxybenzoic acid, phenoxyacetic acid, beta-phenoxypropionic acid, phenoxybenzcic acid, and the like.

As has been stated before, the grease compositions of this invention are formed by combining with the desired lubricating oil an alkali metal salt of a low molecular weight oxy acid with an alkali metal salt of a high molecular weight substantially saturated aliphatic acid. In general, the metallic element of the salts as well as of-the soaps may be any of the alkali metals. Sodium, however, is the preferred embodiment of the invention. It is within the concept of the invention, however, to use mixtures of sodium and lithium, i. e., the sodium salt of the low molecular weight oxy acid may be used in conjunction with the lithium soap of the high molecular weight saturated fatty acid and vice versa.

The relative proportions of the high molecular weight soap and of the low molecular weight salt may be varied rather widely. In molecular proportions, it is preferred to use 1 to 3 parts of the soap with about 1 to 2 parts of the salt. In general, however, it is preferable that the molecular proportions be more nearly equal and specifically, proportions of about 1 to 1 appear to be the most satisfactory. Further, the quantity of the soap and salt ingredients to be used in a given grease composition vary with the type of grease which is desired and also with the kind and the viscosity of the oil which is used as a liquid base. For a stifi grease composition, the total quantity of soap and salt may approach 50% of the weight of the final composition. On the other hand, for a soft grease, the total proportion of soap and salt may be as low as about 5% based on the Weight oi the entire composition.

bricating oil having a viscosity of about 35 to 200 S. U. S. at 210 F. containing about 3 to 30% by weight of the metal soap of a C12 to C22 fatty acid or glyceride along with 2 to 20% by weight of the metal salt of the low molecular weight oxy acid. In general, ethoxypropionic acid is preferred to form the low molecular weight oxy acid portion. However, as it was pointed out above, other oXy acids, such as methoxypropionic acid, propcxypropionic acid, p-methoxybenzoic acid, and the like, may be used.

For ordinary anti-friction bearing greases, the sodium soap and the sodium salt of ethoxypropicnic acid are specifically preferred.

In the preferred embodiment of this invention a substantially saturated fatty acid having an average chain length in the range of 12 to 22 carbon atoms is utilized, however, any of the fatty acids known in the art of grease manufacture may be employed. For ease of dispersion, generally the higher molecular weight acids are preferred. i'hese preferred. acids consist predominantly of acids having a carbon chain length of 18 or slightly higher. They may be natural products such as stearic, arachidic, or the hydrogenated acids obtained from tallow or fish oil acid fractions.

For the liquid phase of the grease, mineral base lubricating oils are preferred but the invention is not necessarily limited to the mineral base oils. Various synthetic oils may also be used. As is well known in the art of grease making, certain synthetic esters, especially the dibasic acid esters, such as di-Z-ethylhexyl sebacate and homologous and analogous esters are preferred for certain purposes in grease making. According to this invention, the lithium soap grease of such compounds, modified with the sodium or lithium salts of ethoxypropionic acid, and the like, are par ticularly useful for lubrication at very low temperatures. Other synthetic oil base greases such as those employing the polyglycols or the glycol ethers are also contemplated as being within the scope of this invention. The combined soaps and salts may be used to thicken mixtures of mineral oil and synthetic oil as well as being useful with either type of oil alone.

As an example of the concept of this invention, a grease composition containing the ethoxypropionic acid and its properties are described below:

EXAMPLE I (a) Formulation Ingredients: Per cent weight Ethoxypropionic acid 6.0 Hydrogenated fish oil acids 15.0 Sodium hydroxide 4.4 Phenyl alpha naphthylamine 1.0 Mineral lub. oil of 500 S. U. S. vis. at

F. (55 at 210 F.) 73.6

(0) Method of preparation The hydrogenated fish oil acids and of the mineral oil were charged to a fire heated grease kettle and the temperature raised to 150 F. The ethoxypropionic acid was charged and the acids immediately coneutralized with a 30% aqueous solution of sodium hydroxide. The temperature was raised to 220 F. and when the soap concentrate was fairly dry additional oil was slowly added while raising the temperature to 440 F. All of the oil should be added by this time. The phenyl-alpha-naphthylamine was added and the grease drawn into p ans for cooling. grease was returned to the kettle for homogenization and then filtered and packaged.

PROPERTIES Percent free alkali"; 0.12 as NaOH Appearance Yellow-smooth short fiber. Dropping point, "F 446 Worked penetration, mm./ 306 Structure stability to mechani- 339 mm./10

cal working penetration after 100,000 strokes fine hole worker plate.

Water washing test, percent loss (125 F. water temperature) Wheel bearing test 6 hours at Pass; conditions and lubrication excellent.

400 hours before bearing High temperature spindle test, 204 bearing, 10,000 E. 1?. Ni,

(0) Method of manufacture The anisic acid, fish oil acid and of the mineral oil were charged to a fire heated grease kettle and heated while agitating to 150 F. The sodium hydroxide as a aqueous solution was added and the soaps formed dehydrated while heating to 300 F. The balance of the mineral oil was then gradually added while continuing to heat to 450 F. At this temperature the phenylalpha-naphthylamine was added and the grease drawn into pans for cooling. (It may be left in the kettle to cool.) When cool the grease was broken down by stirring in the kettle and homogenized. The free reaction of the grease may vary from 0.5% as oleic acid to 0.5% as NaOH. Greases varying between these limits are of excellent structure and stability.

The cold PROPERTIES Penetrations, mm./ 10, 77 F.:

Unworked 200.

Worked, 60 strokes 210.

Worked, 100,000 strokes 255.

(fine hole worker plate).

Dropping point, F 500+.

Water resistance Soluble in boiling water; unaffected at temp. up to 185 F.

EXAMPLE. III

(a) Formulation Ingredients: Percent weight Anisic acid 3.75 iydrogenated fish oil acids 7.50 Sodium hydroxide 2.40 Phenylalpha-naphthylamine 0.75

Mineral lubrication oil of 500 S. U. S. 85.60

viscosity at F. (50 S. U. S. at 210 F.)

(0) Method of manufacture The anisic acid, fish oil acid and of the mineral oil were charged to a fire heated grease kettle and heated while agitating to F. The sodium hydroxide as a 30% aqueous solution was added and the soaps formed dehydrated while heating to 300 F. The balance of the mineral oil was then gradually added while continuing to heat to 450 F. At this temperature the phenylalpha-naphthylamine was added and the grease drawn into pans for cooling. (It may be left in the kettle to cool). When cool the grease was broken down by stirring in the kettle and homogenized. The free acidity of the grease may vary from 0.5% as oleic acid to 0.5% as NaOH. Greases varying between these limits are of eX- cellent structure and stability.

PROPERTIES Penetrations, mm./ 10, '77 F.: y

Unworked 220. Worker, 60 strokes 225. Worked, 100,000 strokes 2'75.

(fine hole worker plate). Dropping point, F 500+ Tendency to displace water on a wet metal surface.

Norma-Hoffman bomb-oxidation; hours to 5 p. s. i. drop at 210 F. (hours).

For comparison, tests on greases having similar formulations but employing furoic, ethoxypropionic, levulinic and caproic acids respectively'are given below:

ilisic FORMULATION 73.6% mineral oil witha viscosity at 210 F. of 500 S. U. 1.0 phenyl-alphanaphthylamine.

P-Methoxy- Ethoxy'probenzoic picnic 233 Levulinic Acid Caproic Acid Acid Acid Percent Free Alkalinity 0.3 0.06.-." 0.25. Worked Penetration (77 F.) 200 234 Greasgc did not ma e.

Structural Stability (Penetration 272 272 Soap separates 100,000 strokes in worker). out. Dropping Point, "F 456 488 Dispersibility oi Soap Excellent... Excellent Fair... WheeJFBearlng Test, 6 hours at Pass 1? Pass Fail The above results show that the sodium soap of low molecular weight oxy acids such as ethoxypropionic acid and p-methoxybenzoic acid in combination with the sodium soap of hydrogenated fish oil acids are easy to disperse and give excellent greases of high dropping point and structural stability.

To summarize briefly, this invention comprises the formation of an improved high temperature lubricating grease composition which consists essentially of a lubricating oil base thickened to a grease consistency with the desired amount of the alkali metal salt of a low molecular weight oxy acid, in conjunction with the alkali metal soap of a high molecular weight saturated aliphatic acid.

What is claimed is:

1. A lubricating grease composition consisting essentially of a lubricating oil thickened to a grease consistency with from 5 to 20% by weight of a mixture of from 1 to 3 parts of an alkali metal soap of a high molecular weight fatty acid and from 1 t 2 parts of an alkali metal salt of a low molecular weight oXy acid having the general formula: 0

RoR'-( :oH

wherein R is selected from the class consisting of mono-valent saturated aliphatic radicals containing from 1 to 5 carbon atoms and R is selected from the class consisting of divalent saturated aliphatic radicals containing from 1 to 5 3. A lubricating grease composition according to claim 1 wherein said low molecular weight oxy acid is methoxypropiom'c acid.

4. A lubricating grease composition according to claim 1 wherein said low molecular weight oxy acid is propoxypropionic acid.

5. A lubricating grease composition consisting essentially of a mineral base lubricating oil thickened to a grease consistency with from 3 to 20% by weight, based on the total composition of an alkali metal soap of a mixture of aliphatic substantially saturated fatty acids having an average carbon chain length within a range of from 12 to 22 carbon atoms and from 2 to 15% by weight of an alkali metal salt of ethoxypropionic acid.

6. A composition according to claim 5 wherein said alkali metal soap is sodium soap and said alkali metal salt is sodium salt. 1

7. A composition as in claim 1 wherein said lubricating oil is a synthetic ester oil.

8. A lubricating grease composition suitable for high temperature service consisting essentially of a lubricating oil thickened to a grease consistency with from 3% to 20% by weight of a mixture of substantially equimolar proportions of an alkali metal salt of ethoxypropionic acid and an alkali metal soap of a mixture of substantially saturated fatty acids having an average carbon chain length within a range from C12 to C22.

9. A composition according to claim 8 wherein said alkali metal salt is sodium salt and wherein said alkali metal soap is sodium soap.

ARNOLD J. MOR'WAY. PAUL V. SMITH, J 11.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,182,137 Rickett Dec. 5, 1939 2,468,098 Morway Apr. 26, 1949 2,487,808 Swenson Nov. 8, 1949 

1. A LUBRICATING GREASE COMPOSITION CONSISTING ESSENTIALLY OF A LUBRICATING OIL THICKENED TO A GREASE CONSISTENCY WITH FROM 5 TO 20% BY WEIGHT OF A MIXTURE OF FROM 1 TO 3 PARTS OF AN ALKALI METAL SOAP OF A HIGH MOLECULAR WEIGHT FATTY ACID AND FROM 1 TO 2 PARTS OF AN ALKALI METAL SALT OF A LOW MOLECULAR WEIGHT OXY ACID HAVING THE GENERAL FORMULA: 